1. Field of the Invention
The present invention relates to an image information transmission system for transmitting image information among a plurality of image information processing units.
2. Description of the Prior Art
Typical prior art image information transmission systems include a loop network system in which a plurality of terminals each having image information forming and recording functions are connected in a loop by a transmission line such as an optical fiber and the image information is transmitted from one of the terminals to other one or more of the terminals and a star network system in which a master station which can distribute an input signal to a plurality of terminals is provided and the output signal from the master station is transmitted to the plurality of terminals. These systems need the transmission of control information called a protocol including a destination terminal address, the number of images to be transmitted and the size of image, from a source terminal of the image information. The transmission of information on the status of the terminal such as a ready for reception signal and an end of reception signal, from the destination terminal to the source terminal is also required.
Such information other than the image information is usually transmitted through the same transmission line as that for the image information, before or after the transmission of the image information.
Control information for indicating an abnormal condition of the unit such as a signal to indicate a jam of a record paper may be generated during the transmission of the image information.
However, if the transmission line is being used to transmit the image information, the control information cannot be transmitted to the source terminal of the image information. As a nature of the image information transmission, a large quantity of information is continuously transmitted through the transmission line. As a result, a long time is required from the occurrence of the abnormal condition during the transmission of the image information to a time point permitted to inform the abnormal condition to the source terminal.
It may be possible to switch the transmission line to the transmission of the control information upon the occurrence of the abnormal condition during the transmission of the image information, but the transmission of the image information to normal terminals is interrupted by the transmission of the control information.